Field of the Invention
The present invention relates to the production of infusible polycarbosilanes and to the conversion of such infusible polycarbosilanes into ceramic articles based on silicon carbide, notably silicon carbide fibers.
Description of the Prior Art
The production of ceramic articles by thermal degradation of organosilicon polymers in a controlled atmosphere is known to this art; numerous literature articles and patents exist on the subject.
One advantage of this "polymer" technique resides, in particular, in the possibilities for shaping this type of product, notably into ceramic silicon carbide fibers, after pyrolysis thereof.
According to the conventional technique, the polymer precursors of polycarbosilane type (possibly after the melting thereof, if originally they are in the solid state) are extruded in the form of continuous fibers (or filaments), which subsequently are treated, in particular to improve their high temperature and/or mechanical strength, and then pyrolyzed in a suitable atmosphere to produce the desired silicon carbide ceramic fiber.
The pretreatment of the fibers prior to pyrolysis, typically designated a hardening, infusibility or cross-linking treatment, is an essential stage in any process for the preparation of ceramic fibers.
At the present time, the hardening of polycarbosilane fibers entails either physical techniques (electronic, UV-irradiation, etc.) or chemical techniques.
The aforementioned physical techniques have the major disadvantage of being awkward and expensive. Therefore, the only economical technique utilized on an industrial scale is chemical hardening by means of an oxygen treatment.
Nonetheless, the introduction of oxygen into silicon carbide fibers presents the drawback of greatly reducing their mechanical strength at application temperatures in excess of 1,000.degree. C.